Massachusetts senator Edward Kennedy told of his fear and remorse surrounding the fateful events on Chappaquiddick Island when his car accident left a woman dead.
'True Compass', a posthumous memoir, will be published on September 14 by Twelve, a division of the Hachette book group.
The 532-page book was obtained early by The New York Times.
In it, Mr Kennedy, 77, who died last week of a brain tumour, said his actions on July 18, 1969, were “inexcusable”.
He said he was afraid and “made terrible decisions” and had to live with the guilt for more than four decades.
Mr Kennedy, who drove off a bridge into a pond, swam to safety while Mary Jo Kopechne drowned.
He later pleaded guilty to leaving the scene of an accident and received a suspended sentence and probation.